1. Field of the Invention
The present invention relates to a starting clutch which can be used in place of a torque converter in a motor vehicle or the like.
2. Related Background Art
Conventionally, in automatic transmissions (ATs), starting of a vehicle has been effected by torque transmission using a torque converter. Since the torque converter has a torque increasing effect and provides smooth torque transmission in increasing and decreasing torque, the torque converter has been incorporated into various vehicles having an automatic transmission.
On the other hand, the torque converter has a disadvantage because it has a great slip amount in increasing and decreasing torque and therefore is not efficient.
Thus, recently, it has been proposed to use a starting clutch in place of the torque converter, and it has been contemplated that torque is amplified by reducing a gear ratio and increasing the number of speed changes.
FIG. 4 is an axial sectional view of a conventional starting clutch. A conventional technique will be described with reference to FIG. 4. A starting clutch 100 includes a multi-plate clutch 101. Within a clutch case 106 of the multi-plate clutch 101, friction plates 102 which are output side friction engaging elements, and separator plates 103 which are input side friction engaging elements are alternately arranged. Further, a backing plate 104 is provided at one end in an axial direction. The backing plate 104 is supported by a stop ring 105 at an axial outer side (left in FIG. 4). On the other hand, at an end opposed to the backing plate 104, there is disposed a piston 108 arranged within the clutch case 106 with an O-ring 107 there between. The piston 108 is biased toward the right by a return spring 116 so that the separator plates 103 and the friction plates 102 are normally brought to a non-engaged condition. Further, an oil chamber 109 is defined between the piston 108 and the clutch case 106.
The starting clutch 100 comprises the multi-plate clutch 101, a housing 110 covering outer periphery of the multi-plate clutch 101, and a damper 117 disposed between the clutch case 106 and the housing 110. The housing 110 is connected to an output shaft 111 of an engine, and the damper 117 is constituted by a spring 130, a retainer plate 113 for holding the spring 130 and a pawl portion 114 for fitting into the spring 130.
In the starting clutch 100, when oil pressure is supplied to the oil chamber 109 through an oil passage 115, the piston 108 is operated to achieve a friction engaging condition.
In the above-mentioned starting clutch 100, a predetermined clearance is provided for the non-engaged or released condition, and, since the clearance is maintained by the biasing force of the return spring against the piston, the torque is completely interrupted.
FIG. 6 is an axial sectional view of a conventional starting clutch (upper half). The starting clutch 50 is includes a damper device 27 and a multi-plate clutch device 11 and is divided into drive side elements and driven side elements. The drive side elements include a connecting portion 21 to an output shaft of an engine, the damper device 27, a housing 20 covering the entire apparatus, a clutch case 16 of the multi-plate clutch 11, and separator plates 13, a backing plate 14, a piston 18 and a base ring 37 which are attached to the clutch case 16. The driven side elements include an output shaft 32, a hub 31 of the multi-plate clutch 11, friction plates 12 and a joint ring 38. The friction plates 12 and the joint ring 38 are attached to a cylindrical portion of the hub 31. The cylindrical portion of the hub 31 and the joint ring 38 are interconnected via a bottom surface 39 extending radially inwardly.
More particularly, the damper device 27 comprises a spring 30, a retainer plate 24 secured to an inner wall of the housing 20 by caulking and adapted to hold the spring 30, and a fitting pawl 23 attached to outer periphery of the clutch case 16. O-rings 17 are disposed between the piston 18 and an inner wall of the clutch case 16 and between the piston 18 and an outer peripheral surface of the base ring 37. There is provided a return spring 26 for biasing the piston 18 toward a releasing direction for the multi-plate clutch (right in FIG. 6), and a member for attaching the return spring 26 is provided on the base ring 37.
The piston 18 is operated by generating oil pressure in an oil chamber 19 by supplying oil through an oil passage 22. Further, a snap ring 15 for supporting the friction plates 12, separator plates 13 and backing plate 14 is arranged an end of an opening of the clutch case 16, and a seal bearing 36 is disposed between the joint ring 38 and the base ring 37. Further, resin washers 40 are disposed between the housing 20 and the hub 31 and between the hub 31 and the base ring 37 and between the clutch case 16 and an oil pump plunger 41.
However, in the conventional technique shown in FIG. 4, since there is the clearance, upon starting the vehicle, when an acceleration pedal is depressed, there arises a timelag (time difference) until the starting clutch is tightened, thereby creating idle charging and shock upon tightening.
To eliminate this, various control methods have been proposed to obtain smooth starting or running of a vehicle by achieving smooth tightening of the clutch upon starting. However, such control is very difficult due to dispersion in number of revolutions of the engine.
Further, in the conventional clutch shown in FIG. 6, problems regarding compactness and weight-reduction of the clutch, which have been investigated in recent technical developments cannot be solved. The present invention provides a starting clutch in which an axial dimension can be reduced, the number of parts can be reduced and the entire construction can be simplified compared to conventional starting clutches.